Question: $ D = \left[\begin{array}{rrr}2 & 1 & 2 \\ 2 & 2 & 0 \\ 2 & 0 & 2\end{array}\right]$ What is $ D^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}-1 & \frac{1}{2} & 1 \\ 1 & 0 & -1 \\ 1 & -\frac{1}{2} & -\frac{1}{2}\end{array}\right]$